Crystal-controlled oscillator and utilization circuit therefor



R. GOLICKE CRYSTAL-CONTROLLED QSCILLATOR AND UTILIZATION CIRCUIT THEREFOR Filed Dec. 15, 1938 Fig-1a 4 lNVENTOR ROMAN 0 /C/ E BY ATTbRNEY Patented Oct. 21, 1941 CRYSTAL-CONTROLLED OSCILLATOR AND UTILIZATION CIRCUIT THEREFOR Roman Golicke, Falkensee, Kreis Osthavelland, Germany, assignor to Fides Gesellschaft fiir die Verwaltung und Verwertung von gewerblichen Schutzrechten m. b. H., Berlin, Germany, a corporation of Germany Application December 15, 1938, Serial No. 245,850 In Germany December 17, 1937 9 Claims. (01. 25036) The present invention relates to a crystal controlled generator having a multi-grid tube. A feature of the invention is that a negative grid is interposed between positive electrodes, preferably grids, and by this arrangement the current distribution is controlled. 7

In accordance with the invention in such tube generators the controlling crystal, usually a quartz crystal, is connected between the negative grid and the positive grid situated nearer to the cathode, and high ohmic grid leak resistors are arranged in circuit with these two grids. The working point is placed in particular in a point of inflection of the characteristic of the grid current of the positive grid such as has been proposed already for maintaining constant the amplitude in generators. The working point is established primarily by a suitable choice of the grid biasing potential of the negative grid.

With the arrangement according to the present invention a tube generator of simplest construction and with a high constancy of the frequency can be provided. Aside from the two grid leak resistors no further circuit elements are required to assure a safe working of the arrangement. Furthermore, no tuning to the frequency of the crystal is necessary. Therefore, the tuning of the plate circuit has no appreciable effect upon the frequency generated, as is the case in the hitherto known crystal controlled generator arrangements. One or both grid leak resistors may, however, also be formed of complex resistors, for instance, by an oscillatory circuit.

In the arrangement according to the present invention, in which the oscillatory crystal is arranged as a connecting member between the two grids, there occurs a feed back in the crystal frequency for which the series member of the chain has ohmic impedance. The control crystal oscillates in series resonance and operatesin the low-ohmic oscillation state so that there exists a lower degree of reaction of the circuit upon the frequency than in the conventional arrangements wherein the tuned plate circuits usually operate in the high-ohmic oscillation state. The crystal employed is preferably so cut that its ohmic resistance is as high as possible, thus affording a favorable matching with the grid leak resistors which the circuit requires. Through this cut the temperature coefficient will be diminished at the same time when using quartz crystals oscillating in the longitudinal axis.

In order to maintain the anode reaction upon the oscillatory circuit as low as possible an auxiliary grid is placed ahead of the anode. This auxiliary grid has the same alternating current potential as that of the cathode.

In the accompanying drawing Figures 1 and 1a show alternative circuit arrangements for a crystal-controlled oscillation generator which exemplifies the invention, and

Fig. 2 shows a circuit arrangement adapted to be used as a frequency standard.

Referring first to Fig. 1, a commercial hexode is therein shown containingthe four gride (Tu-G4, a cathode K and, an anode A. The first and fourth grids G1 and B4 respectively are connected directly to the cathode K. The anode A is supplied with positive potential through a primary winding of transformer T, this primary winding being tuned by a parallel connected capacitor C. Output energy may be taken off from the second ary of the transformer T. Between the cathode and thenegative terminal of an operating supply source (indicated at points land 2) is a resistor R3 and in parallel therewith I preferably dispose a by-pass condenser 5. A frequency-controlling quartz crystal Q is placed in circuit between the positive grid" G2 and the negative. grid G3. The two grids have high-ohmic grid leak resistors R1 and R2 connected thereto. Either circuit as shown in Fig. 1 or in Fig. 13. makes use of the fact thatthe current at the grid Ga of the hexode decreases when the potential at the grid G3 to which a negative biasing potential is applied rises to more positive values. If desired, capacitor 6 may beinserted across the positive and negativeterminals l and 2 of the operating potential source. The modification shown in Fig, 1a isidenticalwith that of Fig. 1 except for the substitution of inductive impedances RL1 and RLz in place of the resistors R1 and R2. If the current passing to the positive grid is compelled to'flow across a resistor R1 of suitable value, and if provision is made for passing potential variations from the positive grid to the successive control grid, a feed back amplifier is obtained which is suited for producing oscillations. The oscillatory quartz crystal situated between the two gridshas a low-ohmic impedance for its natural frequency. Owing to the oscillation performance at the second and third grid of the hexode the plate current of the latter will likewise be frequency-controlled. The output transformer T placed in the anode output can be tuned by the variable condenser C and serves for a more favorable matching of the'hexode output with the load. In contrast to the tuned plate circuit in the ordinary quartz crystal circuits, this output transformer .isnot a component of the oscil latory circuit. The grids G1 and G4 are maintained at cathode potential, since they are directly connected thereto. A further resistor R: is inserted in the cathode circuit. Alternating current is by-passed and direct current is blocked by the condensers 5 and 6.

As already stated, the grid G1 may have a control potentialapplied thereto which is obtained by detection of the output potential so as to influence the characteristic andto obtain the optimum degree of feed back. For the present purpose it is of particular advantage so to dimension the control circuit that only small oscillation amplitudes can appear. The crystal then oscillates with respect to its longitudinal axis which is large in proportion to its thickness.

junction point between resistors 28 and 29 is coupled to the anode A so as to receive an alternating frequency output component from the tube 9. This component is applied unilaterally across the rectifier 21. As the oscillation amplitude increases, the bias supplied to the grid G1 is rendered more negative, thereby tending to stabilize the output from the tube 9 both in The crystal is selected for its small temperature coefficient, high resistance, and smallload capacitance. In suchan arrangement grid current with its reactions detrimental to the constancy of the frequency cannot be produced.

The crystal controlled tube generator in accordance with the present invention is well suited for use as a frequency standard. When using it to this end its output frequency can be utilized in a known manner in frequency multiplication arrangements and in frequency dividers. Thus, for instance, a desired harmonic can be attained from the frequency of the generator in that an auxiliary transmitter whose oscillation circuit is T tuned approximately to the desired frequency is interrupted in the rhythm of the frequency of the generator. Then inthe proximity to the natural frequency of the auxiliary transmitter a series of frequencies having a large amplitude will be obtained, these being whole number multiples of the generator frequency.

'In order to mix a frequency with a multiple of a fundamental frequency that can be chosen at will, it has already been suggested to carry out the superposition in an auxiliary transmitter. Thus, the oscillatory circuit is tuned approximately to the desired frequency range and the production of damped oscillations is caused by repeated interruption in the rhythm of the fundamental frequency.

Fig. 2 hows an example for applying the tube generator according to the present invention as a frequency standard. The multi-grid tube' 9 of the arrangement is used for the oscillatory circuit. The oscillatory arrangement differs slightly from the example shown in Fig. 1 in that the alternating current potential applied to grid G4 across the condenser I0 is the same as that of the cathode. The biasing potential of this grid is tapped at the voltage divider formed by the series of resistors H, l2, l3, l4 and I5. To provide a fine matching of the frequency, a variable condenser I6 is placed in series with the piezo-electric crystal Q. The auxiliary transmitter is hereby coupled across. a condenser-resistor coupling C4 R4.

In order to provide suitable control of the strength of the oscillations generated in the tube 9, thereby to further stabilize the frequency, I find it desirable to rectifya component of the output energy from the oscillator tube and to impress this rectified component upon the first grid G1. This is. accomplished by means of a circuit which includes a biasing source 3| connected between the 'cathode a'nd a rectifier 21 in shunt with whichis aresistor 28. A potential drop occurs across the impedances. 2lfand28 and thispotential is still further, reduced. by a resistor 29 connecting with the grid G1. The

amplitude and in frequency.

The circuit provides a frequency standard in an especially simple and inexpensive way since, for the production of many standard frequencies, only a single control quartz crystal is used. It is true that no gradually variable calibrating frequencies can be attained, but, in the majority of cases, for the calibration of the frequency of transmitters, receivers, frequency meters, and

other high frequency instruments with continuous tuning, this is not required. It is sufiicient, therefore, to confine oneself to a number of sufficiently close fixed standard frequencies. Hence thearrangement according to the invention possesses the advantage that certain frequencies can be checked with greater accuracy.

In the auxiliary transmitter a hexode tube 24 is employed. A feature of this tube is that feed back energy is applied to the first grid G1. The modulation takes place across the third grid G3 to which the output of the control oscillator 9 is applied. A resonant circuit is formed by the variable capacitor C1 in shunt with any selected one of a plurality of inductances L1 having different reactances in order to obtain different ranges of operation. Selection of the desired inductance L1 is madeby means of a multi-throw switch ll. Another multi-throw switch l8 provides a choice of inductances L2 the function of which is to obtain proper regulation of feedback energy arising .in the anode circuit. A third switch I9 is of the double-pole-doublethrow type and is used in position I to obtain a short-circuit across grid leak-resistor 20 between the cathode Kand' ground, while in position 2 the control frequency input is transferred frornthe oscillator 9 to an alternating current source connected across the terminals 3, Q; and at the same time the grid-leak resistor 2| is short-circuited. Furthermore, when switch [9 is moved into position 2 ground potential is applied to capacitors 22 and 23, the other sides of which are connected to the live terminal 4 of the control source. These capacitors 22 and 23 together constitute a capacitive voltage divider which has an attenuating effect in case the control potential becomes too pronounced.

When used as a transmitter the frequency standard furnishes voltages of the order of about 10 millivolts which can be conveniently utilized for the gauging of receivers and frequency meters. j

The apparatus when acting as a receiver can be used for the gauging of transmitters. The latter is possible because the auxiliary transmitter resembles a super-regenerative receiver and operates with the quartz crystal frequency as a pendulum frequency. If at 3', 4 high-frequency input potentials are applied'to' the circuit of the auxiliary transmitter, heterodyning frequencies betweensuch potentials and the multiplied piezo-electric quartz frequency. can be heard in a head piece iii-inserted across the terminals of the secondary'win'ding of the transformer T2; whose primary is in the output circuit of the auxiliary transmitter tube 16. A'galvanometer 25 may be connected to this same output circuit" in; such manner as to observe very low beat frequencies.

Since in the absence of modulation the system of Fig. 2 can be utilized for identifying an incoming frequency, it is also possible to carry out a rough measurement of that frequency to ascertain the existing multiplication factor.

A frequency standard for frequencies lower than the crystal frequency can, furthermore, be obtained if this frequency is used for synchronizing two generators rich in upper harmonics and whose frequency is a whole number fraction of the synchronizing frequency. As such synchronized generators, relaxation circuits may be employed in particular. In order to obtain large proportions of the division it will be admissible among other measures to connect such generators in a cascade such as the following:

Crystal frequency kilocycles 100 First division generator do 10 Second division generator do 1 Third division generator cycles 100 It is also possible to combine division and multiplication stages and to utilize the divided frequencies as a modulation potential for a multiplication stage of the type already cited. In this way in a frequency standard of this kind more gauge points will be obtained in the lower frequency ranges.

The accuracy of this apparatus will be determined primarily by the temperature coefiicients of the quartz crystal. The temperature coeflicient for a 100 kilocycle oscillating quartz crystal is, for instance, 2 cycles per million for 1 C. The accuracy of the frequency standard if a simple thermostat is used or a thermometer plus correction curve would be of the order of one cycle per million.

I claim:

1. An oscillation generator comprising an electron discharge tube having a cathode, an anode, and a plurality of grids of which at least two are positively biased with respect to the cathode and a third grid interposed between said two is negatively biased withrespect to said cathode, a piezo-electric device connected between said third grid and the positively biased grid which intervenes between it and the cathode, means including a direct current source for obtaining said biases and for rendering the anode positive with respect to the cathode, and two grid leak impedances of high ohmic value, one being connected between the positive terminal of said source and that one of said positively biased grids through which electrons pass to the negatively biased grid, the other grid leak impedance being connected between the negative terminal of said source and said negatively biased grid.

2. A generator in accordance with claim 1 wherein the negative bias on said third grid is adjusted to a value such that the working point is in a knee of inflection of the characteristic of this grid with respect to the grid current applicable to the positively biased grid which intervenes between it and the cathode.

3. A generator in accordance with claim 1 and having a variable condenser in series with said piezo-electric device.

4. An oscillation generator comprising an electron discharge tube having a cathode, an anode, and a plurality of grids of which at least two are positively biased with respect to the cathode and a third grid interposed between said two is negatively biased with respect to said cathode, a piezo-electric device connected between said third grid and the positively biased grid which intervenes between it and the cathode, and separate impedances havin high ohmic value and appreciable reactance connected between the cathode and the two grids last mentioned.

5. A generator in accordance with claim 4 wherein a fourth one of said grids is disposed adjacent the anode, this last grid constituting a screen between the anode and the other grids, and a conductive impedance connected in circuit between the fourth grid and the cathode.

6. An oscillation generator comprising an electron discharge tube having a cathode, an anode, grids herein designated #1, #2, #3 and #4 and arranged in that sequence, looking from the cathode toward the anode, means for applying a feed-back potential from the anode to #1 grid with respect to the cathode, means for positively biasing #2 and #4 grids with respect to the cathode, means for negatively biasing #3 grid with respect to the cathode, a piezo-electric device in series with a capacitor and in circuit between #2 grid and #3 grid, and means providing a rectification component of the output potential from said generator which is superposed on said feedback potential for influencing the steepness of the oscillation characteristic.

7. A generator according to claim 6, characterized in that said feed back potential is maintained at a value such that only small oscillation amplitudes can be produced when no grid current flows to the #1 grid and such that a relatively small load is applied to the piezo-electric device.

8. A generator according to claim 6, characterized in that the crystal is so cut that it has a small temperature coefiicient and becomes a high-ohmic resistor.

9. A device for use as a frequency standard comprising an oscillation generator as defined in claim 1 in combination with an auxiliary electron discharge tube stage having an input circuit fed by said generator, said input circuit being tuna- 1e over a range which includes multiples of the oscillation frequency of said piezo-electric device, and means adapted to interrupt the rhythm of said generator frequency, thereby to produce a periodic chain of damped oscillations.

ROMAN GOLICKE. 

